Taste buds in mammals comprise a diverse collection of approximately 100-150 spindle-shaped taste bud cells (=taste cells). Despite years of research, considerable disagreement remains concerning the relationships between taste cell structure and function, including transduction mechanisms and responses to appropriate chemical stimuli. The goal of this grant application is to test the hypothesis that the cells within a taste bud constitute different functional classes of cells and that the cells of each functional class have similar morphological features. The specific aims of this application are to test the following hypotheses using circumvallate and fungiform taste buds of the rat: 1) immunoreactivity to specific biochemical pathway markers (e.g., transducin) is found in specific morphological cell types of rat taste buds. The immunoreactivity of taste cells to specific biochemical pathway markers will be correlated with ultrastructural features of taste cells in the rat (e.g., taste cell type, presence of coated vesicles); 2 taste cells that respond preferentially to a particular chemical stimulus are of one morphological cell type. Electron microscopy will be used to elucidate the ultrastructural features of rat taste cells that have been characterized electrophysiologically using the whole-cell patch clamp recording technique; 3) immunoreactivity to specific biochemical pathway markers is related to a taste cell's electrophysiological responses to applied taste stimuli. A combination of immunocytochemistry and electrophysiology will be used to demonstrate the relationship between the functional features of a taste cell with its biochemical pathways; 4) the distinctive structural and functional features of taste buds, taste cells and their associated synapses derive from both the nature of the receptor cells and the type of innervation. It is predicted that aspects of taste bud ultrastructure are due to the nature of the receptor cell (i.e., circumvallate versus Fungiform), whereas other features may be influenced by the type of innervation (i.e., glossopharyngeal versus Chorda tympani).